The present invention relates to a radar or sonar detection system such as may be used for instance for intruder detection in guarding the perimeter of an area.
In our British application No. 8013259 we have described an intruder detection system in which RF pulses are modulated on a VHF carrier, each RF pulse being modulated with a pseudo-random pulse code sequence and the carrier being transmitted along a length of radiating cable. Signals received from the cable, for example, along a second length of cable disposed substantially parallel to the first length of cable, are correlated with replicas of the code sequence, the replicas being generated under control of a range delay circuit so that the presence of a return signal within a given range cell is detected. The range delay circuit may be arranged so that either a sequence of range cells is cyclically monitored, or a set of parallel code mixers can be used for different range cells so that the signals from all range cells are processed simultaneously.
However, experience with the conventional system has shown that it is rather complicated and, consequently, expensive.